A user needs to run a report in Vault to see all of the documents where a task is assigned to a particular individual. However, the role is assigned to a user group.
The role assignment lists the Group name and not the user that reviews the task.
The Workflow with Document report allows the user to filter by Task Owner. This allows the user to view the tasks to which a particular individual is assigned. The filter also allows the user to filter on the Task Name (optional).
Vault Reporting Documentation: About Workflow & Task Report Fields